1. Field of the Invention
The present invention relates to a carrier for a fuel cell, and a fuel cell catalyst, a membrane-electrode assembly, and a fuel cell system including the same. More particularly, the present invention relates to a carrier for a fuel call having excellent porosity, specific surface area, and density characteristic, and thus being capable of improving catalyst activity due to the excellent catalyst-supporting efficiency and accordingly enhancing cell performance, and a fuel cell catalyst, a membrane-electrode assembly, and a fuel cell system, which all include the same.
2. Description of the Related Art
A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and a fuel such as hydrogen or a hydrocarbon-based material such as methanol, ethanol, natural gas, and the like. Such a fuel cell is a clean energy source that can replace fossil fuels. It includes a stack composed of unit cells and produces various ranges of power output. Since it has a four to ten times higher energy density than a small lithium battery, it has been highlighted as a small portable power source.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell that uses methanol as a fuel.
The polymer electrolyte fuel cell has an advantage of high energy density but also has problems in the need to carefully handle hydrogen gas and in the requirement of accessory facilities such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like in order to produce hydrogen as a fuel gas.
On the contrary, a direct oxidation fuel cell has a lower energy density than the polymer electrolyte fuel cell but has the advantages of easy handling of a fuel, being capable of operating at room temperature due to its low operation temperature characteristic, and no need for an additional fuel reforming processor.
In the above fuel cell, the stack that generates electricity substantially includes several to scores of unit cells stacked in multi-layers. Each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) attached to each other with an electrolyte membrane between them.
A fuel is supplied to the anode and adsorbed on an anode catalyst therein and oxidized to produce protons and electrons. The electrons are transferred into the cathode via an external circuit, while the protons are transferred into the cathode through the polymer electrolyte membrane. In addition, an oxidant is supplied to the cathode. Then, the oxidant, protons, and electrons are reacted on a cathode catalyst to produce electricity along with water.